This invention relates to electronics in general and to liquid crystal displays in particular. More particularly, this invention relates to a brilliant liquid crystal display having the capability of a wide variety of coloration and having an improved contrast ratio.
The advent of liquid crystal display technology has resulted in a wide variety of uses for both digital displays (as in, for example, calculator and digital watch displays), and analog representations (such as are utilized in analog liquid crystal display watches, automotive speedometers, and engine indicators, as well as other applications). Polarized light is used by twisted nematic liquid crystal displays to create light and dark regions of the display, however the absorption of light by the polarizers results in reduced light output.
Dichroic liquid crystal displays or "guest-host" liquid crystal displays utilize dichroic dyes that are in solution with a host liquid crystal. When activated, the liquid crystal host is capable of reorienting the molecules of the dye such that the dyes are essentially nonabsorbing to light entering perpendicular to the surface of the crystal. When the crystal is deactivated, the dye effectively absorbs the incident light. A detailed technical paper entitled "Recent Advances in Dichroic Liquid Crystal Displays for Automotive Applications" by D. Jones and B. Desa was published in the 1981 product catalog of Electronic Display Systems, Inc. and is useful in explaining the operation and principles of dichroic liquid crystal display operation. That technical article is hereby incorporated by reference thereto. That article states that "the colors in the displays shown in FIG. 3 [of the article] are simply the result of silk screening the various pigments onto the back glass". It is suggested, however, that the use of absorptive coloration filters in a liquid crystal display requires increased lighting levels to maintain a desired level of brightness for the display, and alternative methods of coloration are therefore preferable when possible.
Many liquid crystal displays utilize various forms of electroluminescent lighting as an internal light source for dim ambient lighting conditions to enhance the readability of the displays. The book entitled Design Guide: Electroluminescent Lighting, published by Luminescent Lighting Systems, Inc., provides a useful background resource. Chapter 2 is particularly applicable, and is incorporated herein by reference. In paragraph 2.3, page 13 of the incorporated chapter, it is taught that an electroluminescent light, utilized as a common emissive display, may be utilized with a photoluminescent dye or overlay and that absorptive filtering such as utilizing common colored filters should be avoided if possible.